virtualbox.org

I am using older version of VM. I can't upgrade at the moment.

I usually do But when I import the new machine will have the same IP. I know the "official trick" is to remove I even changed mac address, but they will just end up with the same IP again!

What's the correct way doing export so I can prevent this from happening?

I also can't get wireless show up. I probably will make that a separate thread. I use Ubuntu for my host and my guest.
Thanks.

Well it really depends on the version of VirtualBox you are using.
What you are seeing is due to a Linux (feature) that when ever it sees a change in the MAC address it re-assigns the next eth* and retains the original eth0 because they think that you may just be doing this on a whim. Still very annoying but exporting/importing will cause this to happen. Newer versions have a clone feature that allows you to retain the MAC and if you use dhcp will fix this, however if you are using fixed IP addressing you still need to change it if the new guest is on the same LAN.